Apparatus for regulating the recycling of partially combusted fuels in an internal combustion engine

ABSTRACT

In an internal combustion engine having an inlet manifold and an outlet or exhaust pipe, the present apparatus regulates the recycling of partially combusted fuels. The apparatus includes a feedback pipe which connects the exhaust pipe and the intake manifold to permit the exhaust gases to flow from the former to the latter. A cut-off valve is provided in the feedback pipe and is movable therein between first and second positions, the cutoff valve blocking the flow of the partially combusted fuels in the first position and permitting the flow of the latter in the second position. The cut-off valve is electromagnetically controlled by an activating circuit which controls the position of the cut-off valve under different predetermined operating conditions of the combustion engine or the vehicle driven by the combustion engine.

United States Patent 1191 1111 3,807,376

Glockler et al. Apr. 30, 1974 [54] APPARATUS FOR REGULATING THE 3,643,640 2/1972 Kraus etal..... 123/119 A RE Y ()F PARTIALLY COMBUSTED 3,646,764 3/1972 Nakasima et a1... 123/119 A 3,662,722 5/1972 Sarto 123/119 A FUELS IN AN INTERNAL COMBUSTION 3,673,993 7/1972 Nakasima et al. 123/1 19 A ENGINE [75] Inventors: Otto Glockler, Renningen; Dieter FOREIGN PATENTS OR APPLICATIONS Eichler, Hochberg; Willi Game", 830,262 7/1938 France 123/119 A Kornwestheim; Peter Schulzke, Stuttgart; Erich Singer, Besigheim; Primary Examiner-Wendel1 E. Burns Wolfgang S011, Dieburg; Hermann Attorney, Agent, or Firm-Michae1 S. Striker Eisele, Ditzingen, all of Germany [73] Assignee: Robert Bosch GmbH, Stuttgart, ABSTRACT Germany In an internal combustion engine having an inlet mani- [22] Filed: Dec. 17, 1971 fold and an outlet or exhaust pipe, the present apparatus regulates the recycling of partially combusted [2]] Appl' 209220 fuels. The apparatus includes a feedback pipe which connects the exhaust pipe and the intake manifold to [30] Foreign Application Priority Data Permit the exhaust gases to flow from the former to Dec. 17, 1970 Germany 2062067 the A cut-off valve is Provided the feedback Aug. 31, 1971 Germany 2143435 Pipe and is movable herein between first and Second positions, the cut-off valve blocking the flow of the 52 us. 01 123/119 A Partially combusted fuels in the first Peeihen and 51 1111. C1. F02m 25/06 mining flew ef the latter in the Seeehd Peeitieh- [58] Field of Search 123/119 A The cut-eff valve is eleehemagheheahy eehhehed by an activating circuit which controls the position of the [56] References Cited cut-off valve under different predetermined operating UNITED STATES PATENTS conditions of the combustion engine or the vehicle driven by the combustion engine. 3,605,709 9/1971 Nakasima et al. 123/119 A 3,636,934 1/1972 Nakasima et al. 123/119 A 33 Claims, 4 Drawing Figures PATENTEnAPRamsm I I ism-3T6 sum 1 (1F 3 PATENTEDAPMO m4 3.807.376

SHEET 3 [IF 3 APPARATUS Fort REGULATING THE RECYCLING OF PARTIALLY COMBUSTED FUELS IN AN INTERNAL COMBUSTION ENGINE.

According to one embodiment of the, invention, a throttle ,valve is provided in the intake manifold,.said valve being rotatably movable in said manifold for controlling the' amount of air intake into the combustion engine. First andsecond Switches are provided which are, coupled to the throttle valveor to'the gas pedal, which is coupled to the throttle valve,'to open or close ditions of the combustion engine are one of these two' switches closed, such closure activating the transistor switching circuit to cause the electromagnet to position thecut-off valve in, a blocking position. Forpositions of the throttle valve intermediate to idling and forward operations, both switches are open and the cut-off valve maintains its position which permits the flow of the partially combusted fuels in the feedback pipe. According to another embodiment, apivotable baffle plate is provided in the intake manifold upstream of the throttle valve in the direction of intake airflow, the positionof the baffleplatebeing a functionof the quantity of intake air passing into the intake manifold. A swinging lever is coupled to the baffle plate to, share its movements, said swinging lever controlling the open or closed state of the switches. The baffle plate is further coupled to the movable tap of a potentiometer across whicl'i'a voltage is applied. The voltage at the tap point of the potentiometer, being a function of the position of the baffle point, influences a device which controls the injection'of fuel into'the combustion engine.

A threshold circuit may be utilized" which senses the opener closed positions f a, plurality of sensing switches, such as sensing switches which sense the position of the throttle valve- 11g operating temperature of the engine,"the rotationalvelocity of the engine crankshaft, the velocity of the vehicle driven by the engine, and the operating conditions of the transmission. When predetermined conditions are reached for the justmentioned other operating parameters, the threshold circuit activates the electromagnet which controls the cut-off valve in the feedback pipe.

BACKGROUND OF THE INVENTION The present invention relates to recycling systems for internal combustion engines, and particularly to a recycombusted fuels in addition to the products'of combustion. Such exhaust gases contain components which are injurious to'health. In order to reduce the amountof harmful exhaust gases, it hasbeen known to recycle a small amount of the exhaust gases/Thus, a small amount of the exhaust: gases are fed backthrough a feedback conduit to the intake manifold where the exhaustgases are mixed with the fresh air taken into the exhaust manifold. However, this approach has had its disadvantages. For one, the efficiency of the internal combustion engine is generally reduced. Although the reduction in efficiency has not generally been that critical under intermediate operating conditions of the engine, such decrease in efficiency is ,very undesirable when the engine is running under full load or near full load. Also, this approach has causedproblems during idling of the engine, such recycling generally causing rough operation of the engine.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an apparatus for regulating the recycling of partially'combusted fuels which does not have the disadvantages of the prior art.

. It is another object of the present invention to provide an apparatus for regulatingthe recycling of partially combusted fuels in an internal combustion engine which is simple inconstruction-and economical to man- .cling system which utilizes a cut-off valve in the feedufacture.

o It isstill another object of the present invention to provide an apparatus for;regulating the recycling of partially combusted fuels which permits operation of the engine at maximumefficiency at full or near-full operating loads.

It is a further object of the present invention to provide an apparatus for regulating the recycling of par,- tially combusted fuels in combustion engines which does-not cause rough operation of the engine during idling. i V

It is yet a further object of the present invention to provide an apparatusfor regulating the recycling of partially combusted fuels in a combustion engine which regulates the extent of recycling as a function of predetermined loperatingcjonditions of the combustion engine orof the operation of the vehicle driven by the combustion engine.

It is yet another object of the present invention to provide an apparatus for regulating the recycling of partially combusted fuels which simultaneously makes it possible to control the operation of the fuel-injection valves as a function of .the'load conditions of the internal combustion engine. I

In accordance with the present invention, in an internal combustion engine having inlet means and outlet means, an apparatus is provided for regulating and recycling of partially combusted fuels. ,Such apparatus comprises feedback conduit means for passing said partially combusted fuels from said outlet means to said inlet means. Valvemeans are provided in said feedback conduit means for regulating the passage of said partially combusted fuels through said feedback conduit means. The valve means are controlled by. activating means as a function of a predetermned operating condition of said internal combustion engine.

According to a presently preferred embodiment, said valve means comprises a cut-off valve movable between first and second positions, said cut-off valve blocking the flow of partially combusted fuels in said first position and permitting the flow of the latter in said second position. An electromagnetic means is provided for moving said cut-off valve from one of said positions to the other.

Said intake means comprises an intake manifold provided with a movable control element, the position of the latter being directly related to the quantity of air taken into said intake manifold. Switch means are provided which are coupled to said control element to share common movements therewith, said switch means being connected to said activating means, the latter being connected to said electromagnetic means for influencing the position of said cut-off valve in response to predetermined positions of said control element. Namely, said switch means comprise first and second switches. Each switch has a pre-set condition which causes said activating means to influence said electromagnetic means to maintain said cut-off valve in said first position, said pre-set conditions for each switch being attainable by the movement of said control element to said predetermined positions. Said first switch only attains said pre-set condition when said throttle valve is in a position corresponding to idling of said engine, while said second switch only attains said pre-set condition when said throttle valve is in a position corresponding to full load and near-full load operation of said engine. Said control elements can be selected to comprise a throttle valve coupled to a gas pedal, at least one of said switches being coupled to at least one of said throttle valve and said gas pedal. Said electromagnetic means comprises an electromagnetic device having an excitation winding. The activating means comprising a transistor, said switching means being arranged in the base circuit of said transistor and said excitation winding being connected in series with the emitter-collector path of said transistor. Upon actuation of said switches, said excitation winding serves to influence the position of said cut-off valve.

According to another presently preferred embodiment, in addition to said control element, a baffle plate is provided in said intake manifold, at least one of said switches being controlled by the movement of said baffle plate. Said baffle plate is upstream of said control element in the direction of air intake through said intake manifold. Said baffle plate and said control element are arranged in spaced relationship in said intake manifold, said feedback conduit means joining the latter between said baffle plate and said control element. According to a modification, said feedback conduit means joins said intake manifold upstream of said baffle plate in the direction of air intake through said intake manifold. A potentiometer is provided which has a movable tap and is arranged to produce a variable voltage, said control element being connected to said tap contact for assuring movement therewith. Threshold means are connected to said tap contact for responding to at least one predetermined level of said variable voltage. Said activating means further comprises threshold means for detecting a preselected threshold level and having input means. Said first and second switches are connected to said input means. According to further modifications, said threshold circuit further comprises sensitive switch means for operating said threshold circuit, wherein said sensitive switch means may be sensitive to the speed of said combustion engine, the operating temperature of said engine, the

threshold circuit is effective to control the cut-off valve in said feedback conduit means, to thereby regulate the passage of partially combusted fuels from said exhaust pipe to said intake manifold.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional advantages and objects thereof, will best be understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a top-plan view, shown schematically, of an internal combustion engine having fuel injection and recycling of exhaust gases according to the present invention;

FIG. 2 is a schematic of a circuit utilized for automatically controlling the flow of recycled exhaust gases;

FIG. 3 is a second embodiment of the present invention which utilizes an air-measuring device provided in the intake manifold; and

FIG. 4 shows a schematic diagram of a preferred embodiment for a control circuit for controlling the flow of partially combusted fuels from the exhaust pipe to the intake manifold.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a four-cyclinder, four-cycle internal combustion engine 10 is shown which is provided with electromagnetically controlled fuelinjection valves 11. One of the fuel-injection valves is provided in each of the branching pipes which branch from the intake manifold 12 as shown. In the intake manifold is provided a throttle valve 13 which is pivotally mounted in the manifold 12. The throttle valve 13 can be connected to a gas pedal 14 in conventional manner. The throttle valve 13 is pivotable in the intake manifold between two positions. The first position, when the gas pedal 14 is not pressed, this corresponding to the idling condition of the engine, is such that a limited amount of air can enter the intake manifold 12 through the air filter 15. However, when the gas pedal 14 is substantially depressed, the throttle valve 13 opens, that is to say pivots to a position where the maximum amount of air passing through the air filter 15 can pass into the intake manifold. During rotation of the crankshaft of the internal combustion engine, the fuelinjection valves serve to inject gasoline into the combustion engine from fuel conduits (not shown) under a substantially constant pressure of 2 atm. over atmospheric pressure. Such injection results in response to electrical impulses which are provided by an electronic apparatus 17.

The control apparatus 17 may contain a monostable multivibrator which is fired by pulses obtained from an impulse generator (not shown) which is coupled to the crankshaft to thereby generate impulses in synchronism with the position of the crankshaft. By using such pulses from the monostable multivibrator, the duration during which the injection valves are open, and therefore the amount of fuel injected, can be fixed or regulated at will. The adjustment or apportionment of the injected fuel quantities is accomplished by well known means which are not shown. The object of such adjustment is on the one hand to burn the injected fuel fully so as to leave the minimum amount of partially combusted fuels and on the other hand to be able to operate the combustion engine up to the greatest possible power output under full-load operation. As shown, the exhaust pipe 19 is connected to the engine for removal of the exhaust gases, said exhaust pipe 19 being connected to a muffler 20. From the muffler 20 the exhaust gases are released into the atmosphere by means of tailpipe 21.

In order to reduce the amount of harmful constituents in exhaust gases, it has been known, as described above, to feed back a small quantity of the exhaust gas through a feedback pipe from the exhaust pipe 19 to the intake manifold 12. As shown in FIG. 1, the feedback pipe is joined to the intake manifold 12 upstream of the throttle valve 13 in the direction of the air intake into the manifold. The exhaust gases and the freshly drawn-in air are mixed and flowon to the intake manifold 12 for recycling through the engine 10. However, as suggested above, such an arrangement has created problems in the past since recycling during idling has generally caused rough operation of the engine while recycling at full or near-full load has made it impossible to achieve maximum power from the engine.

In order to remove these disadvantages, switches 27 and 28 are provided which may be directly coupled to the gas pedal 14 or to the throttle valve 13 which is coupled to the gas pedal 14. The first switch 27 has a movable arm 31 and a fixed contact 32. The first switch 27 is only closed when the throttle valve 13 is in the position whichcorresponds to idling of the engine. Thus, when the gas pedal 14 is not depressed, the switch 27 is closed or the movable arm 31 engages the fixed contact 32. The second switch 28 similarly has a movable arm 33 and a fixed contact 34. However, the switch 28 is only closed or the movable arm 33 engages the fixed contact 34 when the throttle valve 13 is in a position corresponding to full-load or near-full load operation of the combustion engine. Otherwise, the switch 28 is normally open, said switch closing only when gas pedal 14 is almost totally depressed. As mentioned, in the latter position of the gas pedal, the throttle valve 13 is oriented to permit the maximum amount of air flow through the intake manifold 12.

The switches 27 and 28 form part of a control device, to be described, which controls the flow of exhaust gases in the feedback pipe 25. Namely, it controls the position of the cut-off valve 35. The cut-off valve contains a blocking flap 36 which is controllable by an electromagnetic device 37, to be described, for moving the flap between a position which blocks the flow of exhaust gases through the feedback pipe 25 and a position which permits the maximum flow of exhaust gases through the feedback pipe 25. By controlling the state of excitation of the electromagnetic device 37, it is possible then to regulate the amount of recycling, if any, which takes place.

Referring now to FIG. 2, a circuit schematic is shown of one embodiment of a control device for regulating the electromagnetic device 37 in response to the open or closed states of the switches 27 and 28 referred to in FIG. 1. The active component of the circuit device is a transistor 40 which is provided with a limiting resistor 41 which connects the emitter with the negative voltage supply lead 42. In the collector circuit of the transistor 40 is the excitation winding (not shown) of the electromagnetic device 37. This excitation winding is connected in series with the emitter-collector path of the transistor 40. As shown, the transistor 40 is of the NPN type and the collector circuit is connected to the positive supply voltage lead 44. In order to protect the transistor 40 from voltage spikes which may develop in the excitation winding of the electromagnetic device 37, the winding is shunted by a series circuit comprising a resistance 43 and a diode 45. Such a circuit provides a discharge path for the voltage spikes to thereby protect the transistor 40 from being damaged.

The movable arms 31 and 33 of each of the switches 27 and 28 are connected to the negative voltage supply lead 42 and are thus connected with the emitter of the transistor 40. The fixed contacts 32 and 34 on the other hand are connected to the tap point 47 of a voltage divider, to be described, by means of two diodes 48 and 49. The diodes 48 and 49 efiectively de-couple the switches from one another. As a result of such decoupling between the switches, it is also possible to control the control device and the cut-off valve 35 as functions of other important operating characteristics of the internal combustion engine or of the vehicle powered by said combustion engine. Thus, it may be desired to operate the cut-off valve 35, for example, as the fuel consumption increases at full load or a switching-off during shifting operations.

The voltage divideris positioned between the positive and negative supply voltage leads 44 and 42 respectively. A resistance 50 is connected to the positive supply lead 44 and the resistance 51 is connected to the negative supply lead 42. A series circuit comprising a resistance 54 and a diode 53 is connected in series with and between the resistances 50, 51. The resistance 51 and the cathode of the diode 53 are connected at the junction 52 which is connected to the base of the transistor 40. The connection between the resistances 50 and 54 forms a junction point 47 to which the diodes 48 and 49 are connected.

The operation of the circuit shown in FIG. 2 will now be described. As long as both the switches 28 and 27 are open, the voltage divider comprising the resistances 51, 54 and 50 and the diode 53 establishes a voltage at the junction point 52 which is supplied to the base of the transistor 40. By appropriately selecting the values of the resistances in the divider circuit, a sufficiently positive voltage is applied to the base of the transistor 40 relative to its emitter voltage so that the transistor 40 is placed into a conductive state. Thus, the transistor 40 is biased by the divider circuit, the base current flowing through the resistance 50, the resistance 54 and the diode 53. When the transistor 40 is placed into the conductive state, a collector current flows from the positive supply lead 44 throughthe excitation coil of the electromagnetic device 37, through the collectoremitter path of the transistor 40, the resistance 41 and the negative supply lead 42. By appropriately biasing the transistor 40, a sufficiently large collector current flows which is thus sufficient to excite the electromagnetic device shown in FIG. 1 to thereby change the position of the cut-ofi valve 35. In accordance with one presently preferred embodiment, excitation of the electromagnetic device 37 causes the latter to move the cut-off valve 35 into its open position of the position which permits maximum flow of exhaust gases to be recycled through the feedback pipe 25. As described above, the prevailing operating condition of the engine which causes both switches 27 and 28 to be open is operation at intermediate loads. Thus, with the circuit described, the cut-off valve 35 is closed during idling and at full or near full load, while said valve is open at all intermediate operating conditions.

Describing now the sequence of conditions which take place when the gas pedal 14 is moved to its normal, undepressed condition to its full load, or totally depressed position. When the gas pedal 14 is undepressed, the switch 27 is closed, while the switch 28 is open. This corresponds to the idling. condition of the engine. Referring to FIG. 2, when the switch 27 is closed, the junction point 47 is made more negative by virtue of the connection of the junction point 47 to the negative supply voltage 42 via the diode 49. The diode 49 is placed in the forward conducting state and, therefore, the voltage at the junction point becomes substantially equal to the voltage appearing at the negative voltage supply lead 42, except for the voltage drop across the diode 49. The change in the voltage of the junction point 47 from a substantially positive voltage to a substantially negative voltage results, after further voltage division, in the application of a substantially less positive voltage to the base of the transistor 40. The base of the transistor 40 has its base current reduced substantially, whereby the transistor 40 is turned off or placed in the non-conductive state. With the turning off of the transistor 40, the collector current in the collector of the transistor 40 becomes zero, the current through the electromagnetic device 37 likewise decreases to substantially zero current. With the excitation current in the coil of the electromagnetic device 37 so decreased, said electromagnetic device becomes de-activated, this permitting the cut-off valve 35 to return to its normally closed position. In this latter position, the cut-off valve prevents any of the exhaust gases from being transmitted from the exhaust pipe 19 to the intake manifold 12. To protect the transistor 40 against overloading, in the event that the device 37 is shortcircuited, a series connection of two diodes 56 and 57 is provided between the base of the transistor 40 and the negative supply lead 42. These series-connected diodes are effectively in parallel with the base-emitter path of the transistor 40 and the limiting resistor 41. This provides a parallel current path through the path flowing through the base-emitter terminals. The diodes 56 and 57 are arranged to conduct the current in the same direction as the current flowing through the baseemitter path of the transistor 40.

As the pedal 14 is depressed from its position corresponding to idling of the engine, the switch 27 opens and the transistor suddenly becomes energized or put into the conductive state, and the cut-off valve 35 becomes opened as described above. The cut-off valve 35 in thus maintained open for most positions of the gas pedal 14. However, when the gas pedal 14 is totally depressed, or near totally depressed, this corresponding to full-load or near-full-load operation of the combustion engine, the switch 28 closes. The closing of the switch 28 causes the transistor 40 to be blocked in substantially the same manner as when the switch 27 was closed.

Referring now to FIG. 3, this shows a second embodiment of a similar combustion engine as that shown in FIG. I. Here the fuel-injection valves 11 are shown to be connected to the fuel conduits 61 which supply fuel for injection by the latter. A fuel distributor 62 divides the fuel among the conduits 61. An electric motor driven pump 63 pumps the fuel from the fuel tank to the fuel distributor 62, a pressure regulator 64 being interposed therebetween for maintaining a constant fuel pressure of approximately 2 atm. over atmospheric. Similarly as in the embodiment shown in FIG. 1, this second embodiment is likewise provided with a feedback pipe 25 which is provided with a cut-off valve 35 which is operable by an electromagnetic device 37. A modification in this embodiment, however, is that in addition to the throttle valve 13, a baffle plate 65 is provided in the intake manifold 66 of the internal combustion engine. The baffle plate 65 is biased by a spring (not shown) which urges said baffle plate to move towards blocking position as shown by the solid line in FIG. 3. Said baffle plate 65 is pivotable about an axis 67 and is pivotable about said axis as a function of the quantity of air taken in per unit time into the intake manifold 66. In this sense, the baffle plate 65 comprises an air-measuring device, the intake air causing said plate to move from its blocking position shown when little air is taken into the manifold to its fully opened position when the near-maximum amount of air is drawn in.

With the baffle plate 65, and namely the shaft 67 which pivots the latter, is connected a tap or movable sliding contact 68 which shares the movements of the baffle plate 65. A constant DC. voltage is supplied across the potentiometer 69, said potentiometer having an exponential characteristic curve so that a linear relationship arises between the quantity of air which passes into the intake manifold 66 and the voltage which appears at the tap 68. Such linear voltage is useful for controlling the operation of the injection valves by controlling the control device l7 in synchronization with the speed of the engine.

The baffle plate 65 is also coupled to the swinging lever 72 which controls a first switch 73 and a second switch 74. The swinging lever 72 maintains the switch 73 in an open position when the baffle plate is in its blocking position, such as during idling of the engine. Since the quantity of air intake into the intake manifold 66 is controlled by the throttle valve 13, the baffle plate 65 will remain in its blocked position and the switch 73 will be maintained in the open position so long as the gas pedal 14 is not depressed. This condition is shown in connection with the switch 73 and the solidly drawn baffle plate 65. When the gas pedal is depressed, or the load on the engine is increased, the throttle valve opens so as to permit more air to flow through intake manifold 66, the passing air simultaneously urging the baffle plate 65 to pivot in clockwise direction against the action of the restoring spring (not shown). For example, according to the operating condition of the engine, the baffle plate 65 may assume an angle a, in relation to its fully opened position. Such pivoting movement of the baffle plate 65 causes the swinging lever 72 to rotate clockwise, this permitting the switch 73 to close. The switche 73 remains in the closed position until the engine is returned to its idling condition.

With increased air intake into the intake manifold 66, such as may result from increase of the speed of the engine or further opening of the throttle valve 13, the baffle plate 65 continues to pivot in clockwise direction and may change, for example, from the angle a, to a new angle The position of the baffle plate 65 corresponding to the angle 04 also corresponds to full load or near-full load operation of the combustion engine. In this position of the baffle plate 65, the swinging lever 72 also has pivoted clockwise sufficiently to engage with the movable contact 78 of the switch 74. Thus, the normally closed switch 74 is opened by the swinging lever 72 when the baffle plate 65 has been almost fully opened or when the engine is operating at full or nearfull load.

As described above, the cut-off valve 35 should only be opened when the combustion engine not operating at full load or near full load or at idling conditons. To accomplish this the switches 73 and 74 can be used in conjunction with the circuit shown in FIG. 2. However, the switches 27 and 28 are so arranged so that the switch 27 is normally closed and the switch 28 is normally opened, both switches being opened at operating conditions of the engine which are intermediate to idling and full or near-full load. On the other hand, the switches 73 and 74 in FIG. 3 are arranged so that the switch 73 is normally opened and the switch 74 is normally closed. For intermediate operating conditions of the engine, both switches 73 and 74 are closed. To use the circuit shown in FIG. 2 in conjunction with the embodiment shown in FIG. 3, it may thus be possible to modify the circuit as suggested by the dashed components shown in FIG. 2. In the modified circuit, the switches 27 and 28 as well as the diodes 48 and 49 would be eliminated. The switches 73 and 74 can be connected in series. These switches are then connected to the tap point 47 by means of a coupling circuit such as resistances 48" and 49" connected in series with the diodes 48' and 49'. Although one parallel branch containing the latter resistances and diodes will usually be sufficient, the arrangement shown reduces the current carried in each branch. In this modification, the resistances 51, 54 and 50 are so selected so that the transistor 40 is in a normally non-conductive state. During idling the switch 73 is open while at full or near-full load the switch 74 is open. In these two conditions the voltage level at the tap 47 is maintained at a relatively negative level so that the base voltage of the transistor 40 is not sufficiently positive in relation to its emitter to turn the transistor 40 on. However, at intermediate operating conditions of the internal combustion engine, both switches 73 and 74 close, and since the switches are connected to the positive supply lead 44, a current flows through these switches and through the resistordiode coupling circuit towards the tap point 47. The resistances 48 and 49" are so selected that a sufficiently large current is permitted to flow to make the voltage at the tap point 47 more positive and therefore also make the voltage at the tap point 52 more positive. The divider resistances can be selected so that under the condition where both switches 73 and 74 are closed, the transistor is placed into the conductive state, this energizing the excitation coil of the electromagnetic device 37 to thereby open the cut-off valve 35.

Still referring to FIG. 3, the switches 73 and 74 can be connected to other electronic circuits, the circuit in FIG. 2 being merely illustrative. Control can also be realized with electronic circuitry which senses the voltage U at the output of the movable tap point 68. Thus, the

voltage U can be applied to a threshold circuit which is arranged to detect preselected voltages, these voltaccordance with the characteristics of the potentiometer 69. Being coupled to the baffle plate 65, the voltage U thereby becomes a function of the quantity of air which is taken into the intake manifold 66. Instead of the mechanical switches 73 and 74 shown in FIG. 3, one can also use electronic switches, such as known threshold switches which can be made to open and close similarly as the switches 73 and 74 as a function of the voltage U. Such electronic switches can take the form of a threshold circuit which can comprise an integrated circuit. The threshold switches, as well as other subassemblies in the control device 17 can be selected to be integrated circuits and constructed in modular form for simple construction and maintenance. Additional subassemblies within the control device 17 may include multivibrators, intermediate amplifiers, multiplier stages and other like elements. Such integrated modules can be easily incorporated with one another in well known manner.

Although the feedback pipe 25 in FIG. 3 is shown .to be joined with the intake manifold 66 upstream of the baffle plate 65 in the direction of the air intake, it is equally possible, according to a modification to join such feedback pipe to the intake manifold at a point between the baffle plate 65 and the throttle valve 13, as shown by the dashed outline.

Very frequently, motor vehicles encounter obstacles on the road, this resulting in shocks and vibrations which may affect mechanical components of the vehicle. For this reason, reliable contact of mechanical switches cannot be guaranteed. Additionally, it may be advisable to control the recycling of exhaust gases as a function of the operating temperature of the engine, the ambient temperature, the temperature of the air taken into the intake manifold as well as other operating characteristics of the vehicle, such as the speed of the vehicle. The disadvantages in recycling exhaust gases containing partially combusted fuels may also result or be affected by these enumerated, as well as other operating conditions. To control the position of the cut-off valve as a function of some or all of these conditions, as well as those discussed in connection with FIGS. 1 and 3, a circuit such as shown in FIG. 4 may be utilized. Shown in FIG. 4, are the load-sensitive switches 27 and 28, shown in an intermediate position of load of the engine. In this instance, as described above, both the switches 27 and 28 are opened. The switches 27 and 28 are connected to the input of a direction stage, which can be in form of a threshold circuit, for sensing the opened or closed positions of the switches. In FIG. 4, the detecting circuit is in the form of a Schmitt trigger having an input transistor 81 and an output transistor 82. Additionally, a timing circuit is provided which comprises the capacitor 83 and resistance 84. Positive feedback coupling is utilized, this feedback being provided by connecting the two emitters of the transistors to the negative voltage supply lead 42 through a common-emitter resistance 85. The bases of both of the transistors are directly coupled to the negative voltage supply lead 42. Thus, the base of the transistor 82 is connected to the lead 42 by means of the resistance 87, while the base of the transistor 81 is connected to the lead 42 by way of the resistances 88, 84, and 91. A voltage divider connected between the positive voltage supply lead 44 and the negative voltage supply lead 42 comprises the resistances 91 and 92, said divider having a tap point 90 which is connected to the base of the transistor 81 by way of the resistances 84 and 88. A resistance 86 is connected between the collector of the transistor 81 and the base of the transistor 82.

Also connected to the tap point 90 of the voltage divider is a limiting resistance 93 which is connected in series with the parallel combination of the diodes 47, 48, 94 and 95. Such an arrangement of diodes comprises a four-input OR-circuit. To each of the diodes is connected one of the switches 27, 28, 96 and 97, respectively. The movable contacts of said latter switches are connected to the negative voltage supply lead 42. For purposes of explaining the presently preferred embodiment, only two additional switches, switches 96 and 97, have been shown to be provided in addition to the load-sensitive switches 27 and 28. However, this is only for illustrative purposes, it being understood that additional switches and corresponding diodes can be connected in parallel with the parallel paths shown in FIG. 4 so as to increase the number ofinputs to the OR- circuit. To illustrate the possible applications of such a circuit, the switch 96 can be selected to be a temperature-sensitive switch which is sensitive to the temperature of the internal combustion engine. Preferably, the switch is in the normally closed position, the switch opening when, for example, the operating temperature of the internal combustion engine is equal to or exceeds +lC. Also, the switch 97, in series with the diode 95, can be selected to be sensitive or dependent on a particular operating condition of the motor vehicle which is driven by the internal combustion engine, for example the switch 97 can be dependent on the velocity of the motor vehicle or dependent on a predetermined condition or step of the transmission of the motor vehicle, such as whether the transmission is in overdrive or not. It will be appreciated that all the operating conditions of the internal combustion engine, as well as the conditions relative to the motor vehicle, in most cases either directly or indirectly indicate or influence the load on the engine. For these reasons, these additional conditions may be utilized to supplement or to modify the operation of the basic switches 27 and 28. In other instances, the engine and vehicle characteristics may improve or worsen the performance of the engine in response to the feedback for exhaust gases. For this reason, the latter conditions can likewise be utilized to modify the effects of the switches 27 and 28.

With the circuit shown in FIG. 4, so long as all of the switches 27, 28, 96 and 97 are open, the voltage at the tap point 90 is mostly determined by the voltage dividing resistances 91 and 92. These resistances can be selected so that a voltage at the base of the transistor 81 is sufficiently positive with respect to its emitter so that the transistor 81 is placed into its conductive state. However, when an emitter current flows through the transistor 81, a positive voltage develops across the common-emitter resistance 85, this voltage appearing across the resistance 85 appearing at the emitter of the transistor 82. Additionally, when the transistor 81 conducts, the collector voltage at the latter transistor is very nearly equal to the voltage appearing at the emitter of the transistor 81. The collector voltage of the transistor 81 is transmitted to the base of the transistor 82 by means of the voltage divider circuit which comprises the resistances 86 and 87. By proper selection of the resistances 85, 86 and 87, the emitter of the transistor 82 can be made positive in relation to its base when the transistor 81 is in such conducting state. In this condition, the transistor 82 will be in its non-conductive or cut-off state. The collector circuit of the transistor 82 is connected to a PNP amplifying transistor 100 whose emitter is connected to the positive supply voltage lead 44. When the transistor 82 is in its non-conducting state, the collector voltage of said transistor is substantially equal to the voltage appearing at the positive supply voltage lead 44. For this reason, the base of the transistor 100 is substantially equal to the voltage at the emitter of said transistor, the transistor 100 thereby also being in its non-conducting or cut-off condition. The amplifying transistor 100 is connected to a driving transistor 101, the collector of the former being connected to the base of the latter. The collector of the transistor 101 is provided with an auxiliary relay 102 which operates a switch 102.

When any one of the switches 27, 28, 96 or 97 is closed, one of the respective diodes 47, 48, 94 or is connected to the negative supply voltage lead 42. This places the resistance 93 substantially in parallel with the resistance 91 of the voltage divider circuit. This modification of the voltage dividing circuit is so arranged that on this occurrence the voltage at the tap point 90 becomes substantially less positive. The parallel resistance value of the resistances 91 and 93 are thus so selected that the current flowing through the resistance 92 from the positive supply voltage lead 44 to the negative supply voltage lead 42 takes place through the resulting parallel resistance combination and thus very little base current is permitted to flow into the base of the transistor 81. At such condition, the transistor 81 can no longer conduct current through its collectoremitter path. When the transistor 81 becomes nonconductive, the voltage at the emitters tends to become more negative while the collector of the transistor 81 becomes more positive. Because of the positive feedback utilized, the voltage at the base of the transistor 82 becomes positive with respect to the emitter so that the transistor 82 is switched into its conductive state. Such conduction tends to further block the current through the transistor 81 by reason of the positive voltage appearing across the common-emitter resistance 85. Once conducting, the collector current flowing through the transistor 82 causes a voltage drop to develop across the resistance 103. This voltage difference when applied to the emitter-base junction of the transister-100, is selected to turn this transistor on. In response to the transistor turning on, the collector current flowing through the latter provides the base or biasing current to the driving transistor 101, turning the latter into its conducting state. The resulting current flow in the collector of the transistor 101 energizes the auxiliary relay 102 which closes the switch 102. With the switch 102 closed, the electromagnetic device 37 is provided with the full voltage appearing between the positive and negative voltage supply leads 44 and 42, respectively. As described above, the energization of the electromagnetic device 37 can be utilized to influence the position of the cut-off valve 35.

It may be desirable not to close the cut-off valve 35 instantaneously with the closing of one of the switches 27, 28, 96 or 97. As suggested above, motor vehicles are subjected to vibrations and shocks and it may therefore be desirable to discount the possible effects of such shocks and vibrations on the states of the sensing switches. In this manner, reliable operation of the cutoff valve 35 is assured. In order to discount such spurious effects, a time-delay is provided in the circuit of FIG. 4 which delays the control of the Schmitt trigger comprising the transistors 81 and 82 after one of the sensing switches has been closed. According to the presently preferred embodiment, time delays of approximately between 0.1 and 5 seconds can be selected. The time delay takes place in the following manner. When all of the sensing switches are open, the voltage appearing at the tap poing 90 causes the capacitors 83 to charge to a predetermined level. When one of the sensing switches closes, the voltage at the tap point 90, as described above, tends to become more negative. Although the voltage at the tap point 90 does become more negative almost instantaneously, the voltage at the base of the transistor 81 does not, because of the charge which has been stored on the capacitor 83. The value of the resistance 93 is selected to be much smaller than the value of the resistance 91, so that when one of the switches is closed the placing in parallel of the resistance 93 across the resistance 91 practically short-circuits the latter. Under these conditions the resistance 81 is, for all practical purposes, connected to the negative voltage supply lead 42.'The time constant involved is that determined by the capacitor 83 and the resistance 84 which is used to conduct the stored charge in the capacitor 83 to the negative supply voltage lead 42. Thus, the time constant which may be desired can be adjusted by changing the values of the resistance 84 and/or the capacitor 83.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of applications differing from the types described above.

While the invention has been illustrated and described as embodied-in an apparatus for regulating the recycling of partially combusted fuels, it is not intended to be limited to the various details shown, since various modifications and structural and circuit changes may be made without departing in any way from the spirit and concept of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

l. in an internal combustion engine having inlet means and outlet means, an apparatus for regulating the recycling of partially combusted fuels from said outlet means to said inlet means; valve means provided in said feedback conduit means for regulating the passage of said partially combusted fuels through said feedback conduit means; and activating means for controlling said valve means as a function of a predetermined operating condition of said internal combustion engine, wherein said valve means comprises a cut-off valve movable between first and second positions, said cut-off valve blocking the flow of partially combusted fuels in said first position and permitting the flow of the latter in said second position; and electromagnetic means for moving said cut-off valve from one of said positions to the other, wherein said inlet means comprises an intake manifold and a movably mounted control element in said intake manifold so constructed and mounted as to assume different predetermined positions in dependence upon at least said one operating condition of said engine, and further comprising switch means coupled to said control element for activation in dependence upon the position of said control element, said switch means being connected to said activating means, the latter being connected to said electromagnetic means for influencing the position of said cut-off valve in response to predetermined positions of said control element, wherein said switch means comprises first and second switches, each switch having a pre-set condition which causessaid activating means to influence said electromagnetic means to maintain said cutoff valve in said first position, said pre-set conditions for each switch being attainable by movement of said control element to predetermined positions, said first switch only attaining said pre-set condition when said control element is in a position corresponding to idling of said engine, and said second switch only attaining said pre-set condition when said control element is in a position corresponding to full load and near full load operation of said engine, said activating means further comprising threshold means for detecting a preselected threshold level and having input means, wherein said threshold means comprises an electronic threshold circuit having at least one transistor for sensing said preselected threshold level and said input means including a timing element for delaying the action of said one transistor for at least 0.1 seconds on the occurrence of said level.

2. In an internal combustion engine provided with at least one engine cylinder, an air inlet means leading into said engine cylinder, exhaust-gas outlet means leading out of said cylinder for carrying away exhaust gas, fuel-injection means for injecting predetermined quantities of fuel into said engine cylinder, and a throttle valve in said air inlet means for controlling the flow of air through said air inlet means, in combination therewith, feedback conduit means having one end communicating with said exhaust-gas outlet means and having another end communicating with said air inlet means at a location of said air inlet means upstream of the location of said throttle valve; valve means provided in said feedback conduit means for regulating the passage of said partially combusted fuels through said feedback conduit means; and activating means for con trolling said valve means as a function of a predetermined operating condition of said internal combustion engine.

3. In an internal combustion engine as define in claim 2, wherein said valve means comprises a cut-off valve movable between first and econd positions, said cut-off valve blocking the flow of partially combusted fuels in said first position and permitting the flow of the latter in said second position; and electromagnetic means for moving said cut-ofi valve from one of said positions to the other.

4. In an internal combustion engine as defined in claim 3, wherein said inlet means comprises an intake manifold and movably mounted control means in said intake manifold so constructed and mounted as to assume different predetermined positions in dependence upon at least said one operating condition of said engine, and further comprising switch means coupled to said control means for activation in dependence upon the position of said control element, said switch means being connected to said activating means, the latter being connected to said electromagnetic means for influencing the position of said cutoff valve in response to predetermined positions of said control means.

5. In an internal combustion engine as defined in claim 4, wherein said switch means comprises first and second switches, each switch having a pre-set condition which causes said activating means to influence said electromagnetic means to maintain said cutoff valve in said first position, said pre-set conditions for each switch being attainable by the movement of said control means to predetermined positions, said first switch only attaining said pre-set condition when said control means is in a position corresponding to idling of said engine, and said second switch only attaining said preset condition when said control means is in a position corresponding to full load and near full load operation of said engine.

6. In an internal combustion engine as defined in claim 5, wherein said control means comprises said throttle valve, said switches being coupled to said throttle valve.

7. In an internal combustion engine as defined in claim 5, said control means comprising a movable airflow sensing baffle plate provided in said intake manifold, said switches being controllable by the movement of said baffle plate.

8. In an internal combustion engine as defined in claim 7, wherein said movable airflow-sensing baffle plate comprises a pivotable flap member.

9. In an internal combustion engine as defined in claim 5, wherein said electromagnetic means comprises an electromagnetic device having an excitation winding, said activating means comprising a transistor, said switching means being arranged in the base circuit of said transistor, said excitating winding being connected in series with the emitter-collector path of said transistor, said excitation winding winding serving to influence the position of said cutoff valve.

10. In an internal combution engine as defined in claim 9, wherein each switch has first and second contacts, said first contact being connected to the emitter of said transistor, said activating means further comprising voltage divider means operable under the same supply voltage as the series emitter-collector circuits, said divider means having at least one tap point, the base of said transistor being connected to said tap point, said second contacts being also connected to said divider means.

11. In an internal combustion engine as defined in claim 10, wherein said activating means further comprises two diodes connecting said second contacts to said divider means.

12. In an internal combustion engine as defined in claim 11, wherein said divider means comprises at least two series resistances.

13. In an internal combustion engine as defined in claim 12, wherein said divider means comprises three resistances and a diode connected in series, said divider means having two tap points, said base of said transistor being connected to one tap point and said second contacts being connected to the other tap point.

14. In an internal combustion engine as defined in claim 9, wherein said activating means has a supply lead, a limiting resistor being connected between the emitter and said lead, and two series connected diodes connected between the base and said lead to thereby form a parallel conduction path to the base-emitter path of said transistor, said two diodes being arranged to conduct currents in the same direction as can flow in the base-emitter path of said transistor.

15. In an internal combustion engine as defined in claim 7, said throttle valve being located downstream of said control means.

16. In an internal combustion engine as defined in claim 4, wherein said control means comprises a movable airflow-sensing baffle plate located in said intake manifold.

17. In an internal combustion engine as defined in claim 15, wherein said baffle plate and said control means are arranged in spaced relationship in said intake manifold, said feedback conduit means joining the latter between said baffle plate and said control means.

18. In an internal combustion engine as defined in claim 15, wherein said feedback conduit means joins said intake manifold upstream of said baffle plate in the direction of air intake through said intake manifold.

19. In aninternal combustion engine as defined in claim 4, further comprising potentiometer means having a movable tap contact arranged to produce variable voltage levels said control means being connected to said tap contact for sharing movement therewith; and treshold means connected to said tap contact for responding to at least one predetermined level of said variable voltage.

20. In an internal combustion engine as defined in claim 5, said activating means further comprising threshold means for detecting a preselected threshold level and having input means, said first and second switches being connected to said input means.

21. In an internal combustion engine as defined in claim 1, said threshold circuit comprising two transistors, positive feedback coupling being used to connect said transistors.

22. In an internal combustion engine as defined in claim 21, wherein the emitters of said two transistors are connected to one another, said threshold circuit I further comprising an emitter resistance connecting said connected emitters with a voltage supply lead of said circuit.

23. In an internal combustion engine as defined in claim 22, said threshold circuit further comprising base resistances connecting each of the bases of said two transistors with said supply lead.

24. In an internal combustion engine as defined in claim 22, said threshold circuit further comprising a direct feedback coupling component connecting the collector of said one transistor and the base of the other transsistor.

25. In an internal combustion engine as defined in claim 24, wherein said component is a resistance.

26. In an internal combustion engine as defined in claim 24, said threshold circuit further comprising a divider circuit connected between the voltage supply leads and having a tap point, the base of said one transistor beingconnected to said tap point, and diodes connecting said first and second switches to said tap point.

27. In an internal combustion engine as defined in claim 26, said threshold circuit further comprising temperature sensitive switch means sensitive to the operating temperature of said engine; and a diode connecting said temperature sensitive switch to said tap point.

28. In an internal combustion engine as defined in claim 26, said threshold circuit further comprising sensitive switch means; and a diode connecting said sensitive switch means to said tap point.

29. In an internal combustion engine as defined in claim 28, wherein said sensitive switch means is sensitive to the speed of said combustion engine.

30. In an internal combustion engine as defined in claim 28, wherein said sensitive switch means is sensitive to the speed of the vehicle powered by said combustion engine.

31. In an internal combustion engine as defined in claim 28, wherein said sensitive switch means is sensitive to the operating conditions of the transmission of the vehicle powered by said combustion engine.

32. In an internal combustion engine as defined in claim 1, wherein said timing element comprises at least a capacitor connected in parallel with the emitter-base path of said one transistor.

33. In an internal combustion engine as defined in claim 32, wherein said switches are connected to the base of said one transistor. 

1. In an internal combustion engine having inlet means and outlet means, an apparatus for regulating the recycling of partially combusted fuels from said outlet means to said inlet means; valve means provided in said feedback conduit means for regulating the passage of said partially combusted fuels through said feedback conduit means; and activating means for controlling said valve means as a function of a predetermined operating condition of said internal combustion engine, wherein said valve means comprises a cut-off valve movable between first and second positions, said cut-off valve blocking the flow of partially combusted fuels in said first position and permitting the flow of the latter in said second position; and electromagnetic means for moving said cut-off valve from one of said positions to the other, wherein said inlet means comprises an intake manifold and a movably mounted control element in said intake manifold so constructed and mounted as to assume different predetermined positions in dependence upon at least said one operating condition of said engine, and further comprising switch means coupled to said control element for activation in dependence upon the position of said control element, said switch means being connected to said activating means, the latter being connected to said electromagnetic means for influencing the position of said cut-off valve in response to predetermined positions of said control element, wherein said switch means comprises first and second switches, each switch having a pre-set condition which causes said activating means to influence said electromagnetic means to maintain said cut-off valve in said first position, said pre-set conditions for each switch being attainable by movement of said control element to predetermined positions, said first switch only attaining said pre-set condition when said control element is in a position corresponding to idling of said engine, and said second switch only attaining said pre-set condition when said control element is in a position corresponding to full load and near full load operation of said engine, said activating means further comprising threshold means for detecting a preselected threshold level and having input means, wherein said threshold means comprises an electronic threshold circuit having at least one transistor for sensing said preselected threshold level and said input means including a timing element for delaying the action of said one transistor for at least 0.1 seconds on the occurrence of said level.
 2. In an internal combustion engine provided with at least one engine cylinder, an air inlet means leading into said engine cylinder, exhaust-gas outlet means leading out of said cylinder for carrying away exhaust gas, fuel-injection means for injecting predetermined quantities of fuel into said engine cylinder, and a throttle valve in said air inlet means for controlling the flow of air through said air inlet means, in combination therewith, feedback conduit means having one end communicating with said exhaust-gas outlet means and having another end communicating with said air inlet means at a location of said air inlet means upstream of the location of said throttle valve; valve means provided in said feedback conduit means for regulating the passage of said partially combusted fuels through said feedback conduit means; and activating means for controlling said valve means as a function of a predetermined operating condition of said internal combustion engine.
 3. In an internal combustion engine as define in claim 2, wherein said valve means comprises a cut-off valve movable between first and econd positions, said cut-off valve blocking the flow of partially combusted fuels in said first position and permitting the flow of the latter in said second position; and electromagnetic means for moving said cut-off valve from one of said positions to the other.
 4. In an internal combustion engine as defined in claim 3, wherein said inlet means comprises an intake manifold and movably mounted control means in said intake manifold so constructed and mounted as to assume different predetermined positions in dependence upon at least said one operating condition of said engine, and further comprising switch means coupled to said control means for activation in dependence upon the position of said control element, said switch means being connected to said activating means, the latter being connected to said electromagnetic means for influencing the position of said cutoff valve in response to predetermined positions of said control Means.
 5. In an internal combustion engine as defined in claim 4, wherein said switch means comprises first and second switches, each switch having a pre-set condition which causes said activating means to influence said electromagnetic means to maintain said cutoff valve in said first position, said pre-set conditions for each switch being attainable by the movement of said control means to predetermined positions, said first switch only attaining said pre-set condition when said control means is in a position corresponding to idling of said engine, and said second switch only attaining said pre-set condition when said control means is in a position corresponding to full load and near full load operation of said engine.
 6. In an internal combustion engine as defined in claim 5, wherein said control means comprises said throttle valve, said switches being coupled to said throttle valve.
 7. In an internal combustion engine as defined in claim 5, said control means comprising a movable airflow sensing baffle plate provided in said intake manifold, said switches being controllable by the movement of said baffle plate.
 8. In an internal combustion engine as defined in claim 7, wherein said movable airflow-sensing baffle plate comprises a pivotable flap member.
 9. In an internal combustion engine as defined in claim 5, wherein said electromagnetic means comprises an electromagnetic device having an excitation winding, said activating means comprising a transistor, said switching means being arranged in the base circuit of said transistor, said excitating winding being connected in series with the emitter-collector path of said transistor, said excitation winding winding serving to influence the position of said cutoff valve.
 10. In an internal combution engine as defined in claim 9, wherein each switch has first and second contacts, said first contact being connected to the emitter of said transistor, said activating means further comprising voltage divider means operable under the same supply voltage as the series emitter-collector circuits, said divider means having at least one tap point, the base of said transistor being connected to said tap point, said second contacts being also connected to said divider means.
 11. In an internal combustion engine as defined in claim 10, wherein said activating means further comprises two diodes connecting said second contacts to said divider means.
 12. In an internal combustion engine as defined in claim 11, wherein said divider means comprises at least two series resistances.
 13. In an internal combustion engine as defined in claim 12, wherein said divider means comprises three resistances and a diode connected in series, said divider means having two tap points, said base of said transistor being connected to one tap point and said second contacts being connected to the other tap point.
 14. In an internal combustion engine as defined in claim 9, wherein said activating means has a supply lead, a limiting resistor being connected between the emitter and said lead, and two series connected diodes connected between the base and said lead to thereby form a parallel conduction path to the base-emitter path of said transistor, said two diodes being arranged to conduct currents in the same direction as can flow in the base-emitter path of said transistor.
 15. In an internal combustion engine as defined in claim 7, said throttle valve being located downstream of said control means.
 16. In an internal combustion engine as defined in claim 4, wherein said control means comprises a movable airflow-sensing baffle plate located in said intake manifold.
 17. In an internal combustion engine as defined in claim 15, wherein said baffle plate and said control means are arranged in spaced relationship in said intake manifold, said feedback conduit means joining the latter between said baffle plate and said control means.
 18. In an internal combustion engine as defined in claim 15, whereiN said feedback conduit means joins said intake manifold upstream of said baffle plate in the direction of air intake through said intake manifold.
 19. In an internal combustion engine as defined in claim 4, further comprising potentiometer means having a movable tap contact arranged to produce variable voltage levels said control means being connected to said tap contact for sharing movement therewith; and treshold means connected to said tap contact for responding to at least one predetermined level of said variable voltage.
 20. In an internal combustion engine as defined in claim 5, said activating means further comprising threshold means for detecting a preselected threshold level and having input means, said first and second switches being connected to said input means.
 21. In an internal combustion engine as defined in claim 1, said threshold circuit comprising two transistors, positive feedback coupling being used to connect said transistors.
 22. In an internal combustion engine as defined in claim 21, wherein the emitters of said two transistors are connected to one another, said threshold circuit further comprising an emitter resistance connecting said connected emitters with a voltage supply lead of said circuit.
 23. In an internal combustion engine as defined in claim 22, said threshold circuit further comprising base resistances connecting each of the bases of said two transistors with said supply lead.
 24. In an internal combustion engine as defined in claim 22, said threshold circuit further comprising a direct feedback coupling component connecting the collector of said one transistor and the base of the other transsistor.
 25. In an internal combustion engine as defined in claim 24, wherein said component is a resistance.
 26. In an internal combustion engine as defined in claim 24, said threshold circuit further comprising a divider circuit connected between the voltage supply leads and having a tap point, the base of said one transistor being connected to said tap point, and diodes connecting said first and second switches to said tap point.
 27. In an internal combustion engine as defined in claim 26, said threshold circuit further comprising temperature sensitive switch means sensitive to the operating temperature of said engine; and a diode connecting said temperature sensitive switch to said tap point.
 28. In an internal combustion engine as defined in claim 26, said threshold circuit further comprising sensitive switch means; and a diode connecting said sensitive switch means to said tap point.
 29. In an internal combustion engine as defined in claim 28, wherein said sensitive switch means is sensitive to the speed of said combustion engine.
 30. In an internal combustion engine as defined in claim 28, wherein said sensitive switch means is sensitive to the speed of the vehicle powered by said combustion engine.
 31. In an internal combustion engine as defined in claim 28, wherein said sensitive switch means is sensitive to the operating conditions of the transmission of the vehicle powered by said combustion engine.
 32. In an internal combustion engine as defined in claim 1, wherein said timing element comprises at least a capacitor connected in parallel with the emitter-base path of said one transistor.
 33. In an internal combustion engine as defined in claim 32, wherein said switches are connected to the base of said one transistor. 